Error Deserializing Struct With `flatten`-ed Tagged Enum

#### Version

Tested on both `v1.1.6` and `master` branch.

#### Briefly describe the bug.

Deserializing a struct with a flattened tagged enum field does not seem to work.

#### Include a complete program demonstrating a problem.

Code:

```rust
#![allow(dead_code)]

use serde::de::DeserializeOwned;
use std::fmt::Debug;

mod tagged_enum {
use serde::Deserialize;

#[derive(Debug, Deserialize)]
pub struct Record {
common: u64,
#[serde(flatten)]
kind: Kind,
}

#[derive(Debug, Deserialize)]
#[serde(tag = "kind", content = "parameter", rename_all = "lowercase")]
enum Kind {
Foo(u64),
Bar(bool),
}
}

mod flattened_struct {
use serde::Deserialize;

#[derive(Debug, Deserialize)]
pub struct Record {
common: u64,
#[serde(flatten)]
inner: Inner,
}

#[derive(Debug, Deserialize)]
struct Inner {
kind: Kind,
parameter: Value,
}

#[derive(Debug, Deserialize)]
#[serde(rename_all = "lowercase")]
enum Kind {
Foo,
Bar,
}

#[derive(Debug, Deserialize)]
#[serde(untagged)]
enum Value {
Num(u64),
Bool(bool),
}
}

const CSV: &[u8] = b"\
common,kind,parameter
1,foo,42
2,bar,true";

fn dbg_records()
where
T: Debug + DeserializeOwned,
{
let mut reader = csv::Reader::from_reader(CSV);
for record in reader.deserialize::() {
println!("{:#?}", record);
}
}

fn main() {
dbg_records::(); // Error!
dbg_records::(); // OK.
}
```

([Playground link](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=a7006934525c7c22b7acf68d9bd058cc)).

#### What is the observed behavior of the code above?

Fails to deserialize with invalid type: byte array, expected "kind", "parameter", or other ignored fields error:

```
Err(
Error(
Deserialize {
pos: Some(
Position {
byte: 22,
line: 2,
record: 1,
},
),
err: DeserializeError {
field: None,
kind: Message(
"invalid type: byte array, expected \"kind\", \"parameter\", or other ignored fields",
),
},
},
),
)
Err(
Error(
Deserialize {
pos: Some(
Position {
byte: 31,
line: 3,
record: 2,
},
),
err: DeserializeError {
field: None,
kind: Message(
"invalid type: byte array, expected \"kind\", \"parameter\", or other ignored fields",
),
},
},
),
)
```

#### What is the expected or desired behavior of the code above?

To correctly deserialize records as they are done in the case of flattened structs (also included in code example).